Dyes have been widely used as colorants for oil-based ballpoint pen inks. In cases where dyes are used as colorants, however, the writing produced with such inks tends to have poor light resistance. To improve the light resistance of writing, the dispersion of a pigment in an oil-based ballpoint pen ink has been studied. Dispersing a pigment in an oil-based ballpoint pen ink, however, causes some other problems. For example, writing becomes difficult or the ball seat becomes worn because of pigment settling or aggregation occurring with time.
To overcome such problems caused by the use of pigments, particularly to suppress the wear of the ball seat, Patent Document 1, for example proposes an ink composition wherein a pigment is dispersed in an oil-based component in advance and then a water-based component containing a lubricant is solubilized in the oil-based component.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2004-115611